Emissions Trading Scheme (ETS)
Governments have two levers to put a price on carbon. One sets the price directly and lets emissions find their own level — a carbon tax. The other does the opposite: it fixes the quantity of emissions allowed, hands out a matching number of tradable permits, and lets the market discover the price. That second lever is the emissions trading scheme, and it now governs the compliance carbon cost of power stations, steelworks, cement kilns, refineries, and airlines across the European Union, the United Kingdom, China, California, and a dozen other jurisdictions.
An ETS changes what a tonne of carbon costs you — it does not change how many tonnes you report.
An emissions trading scheme (ETS), or cap-and-trade, caps total emissions from covered sectors, issues a matching quantity of tradable allowances (one = one tonne of CO₂e), and makes each installation surrender one per tonne emitted. The cap falls yearly.
Definition — How Cap-and-Trade Works
An emissions trading scheme is a market-based instrument that limits greenhouse gas emissions by capping the total quantity a group of covered emitters may release, then letting those emitters trade a fixed pool of emission allowances among themselves. It is the reason “cap-and-trade” and “emissions trading” are used interchangeably: the regulator sets the cap, and the market does the trade.
The mechanism is deliberately indirect. Rather than telling each factory how much it may emit, the regulator issues a total number of allowances equal to the cap — each allowance a licence to emit one tonne of carbon-dioxide-equivalent. At the end of each compliance year every covered installation must hand back (“surrender”) one allowance for every tonne it actually emitted. A firm that can cut emissions cheaply sells its spare allowances; a firm that cannot buys them. Abatement therefore happens first wherever it is cheapest across the whole system, and the price that clears the market — the carbon price — settles at the marginal cost of the last tonne of reduction needed to meet the cap.
An ETS fixes the environmental outcome (the cap) and lets the price float. A carbon tax fixes the price and lets the quantity of emissions float. This “quantity instrument vs price instrument” distinction is the single most important thing to understand about the term — everything else follows from it.
The Building Blocks of an ETS
Every compliance emissions trading scheme, from the EU ETS to China’s national market, is assembled from the same five components:
- A cap. A legally binding ceiling on total emissions from covered installations, expressed in tonnes of CO₂e. The cap is the environmental promise of the scheme.
- Allowances. The cap is divided into tradable units — one allowance = one tonne of CO₂e. The EU calls its unit the EU Allowance (EUA); the UK, the UK Allowance (UKA).
- A surrender obligation. Each covered installation must monitor, report, and verify its emissions, then surrender one allowance per tonne by an annual deadline. Falling short triggers a penalty — in the EU ETS, €100 per missing tonne and the obligation to surrender the allowance anyway.
- A trading market. Allowances can be bought, sold, and banked, so the abatement burden flows to the lowest-cost emitters and a transparent carbon price emerges.
- A declining cap. The ceiling is reduced every year by a linear reduction factor, tightening allowance supply over time so the carbon price rises and the emissions trajectory bends toward the jurisdiction’s climate target.
The EU labels its programme a “System” (EU ETS = EU Emissions Trading System) and the UK a “Scheme” (UK ETS = UK Emissions Trading Scheme). They are the same class of instrument — the word choice is jurisdictional, not technical.
ETS vs a Carbon Tax — Quantity vs Price
An ETS and a carbon tax are the two principal forms of carbon pricing, and they are mirror images. A carbon tax names the price and accepts whatever emission reduction that price delivers. An ETS names the emission reduction — the cap — and accepts whatever price the market sets to hit it.
| Dimension | Emissions Trading Scheme | Carbon Tax |
|---|---|---|
| Instrument type | Quantity — caps tonnes | Price — sets cost per tonne |
| What the government fixes | The cap (the outcome) | The price per tonne |
| What the market decides | The carbon price | The emissions achieved |
| Price discovery | Trading of allowances | Set by legislation / schedule |
| Price certainty | Lower — price can be volatile | Higher — price is fixed |
| Emissions certainty | Higher — the cap is binding | Lower — depends on response |
| Live examples | EU ETS, UK ETS, China national ETS | Singapore Carbon Tax, carbon levies |
| GreenCalculus tool | EU ETS Allowance Calculator | Carbon Tax Liability Calculator |
In practice many jurisdictions run both, or bolt price controls onto an ETS — a price floor at auction, or a cost-containment reserve released when prices spike — so the two instruments increasingly borrow each other’s features. The dividing line remains what is fixed first: the tonnes, or the price.
Allowances, Allocation, and the Carbon Price
How allowances reach emitters shapes both the fairness and the price signal of a scheme. There are two routes, usually used together:
Auctioning
The regulator sells allowances to the highest bidders. This is the default in the power sector, where costs can be passed through to electricity prices. Auction revenue typically funds decarbonisation programmes.
Free allocation
Allowances are handed out at no charge, usually by a product benchmark, to trade-exposed industries such as steel, cement, and chemicals. The aim is to blunt “carbon leakage” — production relocating to jurisdictions with no carbon price.
Two further features govern how the price behaves over time. Banking lets firms carry unused allowances into future years, smoothing the price and rewarding early abatement. Supply adjustment mechanisms — the EU’s Market Stability Reserve is the best-known — withdraw or release allowances to dampen the surpluses and shortages that would otherwise whipsaw the price.
Because the marginal carbon price an ETS produces is a real, observable market signal, companies increasingly use it as the anchor for an internal carbon price and to decide which abatement projects clear the bar on a marginal abatement cost curve — any measure that abates a tonne for less than the allowance price is worth doing before buying the allowance. The EU carbon price is also the reference the Carbon Border Adjustment Mechanism (CBAM) uses to charge imports, extending the ETS price to goods produced outside the bloc.
Allowances are denominated in tonnes of CO₂e and priced in currency per tonne (€/tCO₂e for an EUA, £/tCO₂e for a UKA). CO₂e aggregates each gas by its global warming potential — methane at 29.8 [GreenCalculus gwp.CH4_fossil.ar6_100 · IPCC AR6 · v2026.272] and nitrous oxide at 273 [GreenCalculus gwp.N2O.ar6_100 · IPCC AR6 WGI Ch 7 Table 7.SM.7 (2021) — AR6 GWP-100] times CO₂ over 100 years on the current AR6 basis. Each scheme fixes the GWP set it uses in its own monitoring regulation — the EU ETS still applies AR5 GWP-100 values for compliance — so always read the allowance quantity on the basis its regulation specifies, not the corporate-reporting default.
Major Emissions Trading Schemes Today
The EU launched the world’s first major cap-and-trade programme in 2005, and the model has since spread across every populated continent. According to the World Bank Carbon Pricing Dashboard, emissions trading schemes and carbon taxes together now cover roughly a quarter of global greenhouse gas emissions.
| Scheme | Launched | Principal coverage | Allowance |
|---|---|---|---|
| EU ETS | 2005 | Power, heavy industry, intra-EEA aviation, maritime (from 2024) | EUA |
| UK ETS | 2021 | Power, energy-intensive industry, domestic + departing aviation | UKA |
| China national ETS | 2021 | Power generation — the largest scheme by covered emissions | CEA |
| California Cap-and-Trade | 2013 | Power, industry, transport & heating fuels (linked with Quebec) | CCA |
| RGGI (US Northeast) | 2009 | Power sector across participating states | — |
| Korea K-ETS | 2015 | Power, industry, buildings, aviation, waste | KAU |
| New Zealand ETS | 2008 | Energy, industry, transport, waste, forestry | NZU |
The EU is extending the model to a second system, “ETS2”, covering fuel used in buildings, road transport, and small industry from 2027 — a sign that cap-and-trade is moving beyond the large industrial installations it began with.
How an ETS Fits GHG Accounting
This is where practitioners most often go wrong, so it is worth stating plainly. An emissions trading scheme is a compliance and financial obligation layered on top of a company’s greenhouse gas inventory — it is not part of the inventory itself. The tonnes an installation emits are recorded as its Scope 1 emissions under the GHG Protocol regardless of how many allowances it holds, buys, or surrenders.
Buying or surrendering allowances does not reduce reported emissions. If a plant emits 500,000 tonnes and surrenders 500,000 allowances, it still reports 500,000 tonnes of Scope 1 — the allowances are the price it paid, not a reduction it achieved. Allowances, like carbon offsets, are accounted for separately from the gross inventory and are never subtracted from it. The only thing that lowers reported Scope 1 is emitting fewer tonnes.
The distinction matters for disclosure as much as for inventory integrity. Frameworks such as the CSRD/ESRS E1 and IFRS S2 ask companies to report gross emissions and to disclose their exposure to carbon-pricing schemes — the allowances held, the compliance cost, and the financial risk of a rising carbon price — as two separate things. Collapsing them understates the physical footprint and obscures the transition risk.
Worked Micro-Example
A cement installation covered by the EU ETS has verified emissions of 500,000 tCO₂e for the 2025 compliance year. Because cement is trade-exposed, it receives 380,000 free allowances against a product benchmark and must obtain the remainder on the market.
Surrender obligation = 500,000 EUAs (one per tonne emitted)
Free allocation = 380,000 EUAs
Allowances to purchase = 500,000 − 380,000 = 120,000 EUAs
Compliance cost = 120,000 × €70/tCO₂e = €8.4 million (€70 is an illustrative allowance price, hardcoded for this example — the live price is set by the market)
Reported Scope 1 emissions = 500,000 tCO₂e — unchanged
The €8.4 million is a real cost that flows through the profit-and-loss account and belongs in the company’s transition-risk disclosure. The 500,000 tonnes is what appears in the GHG inventory. The two numbers describe different things and must never be blended. Run the full allowance-cost and free-allocation calculation in the EU ETS Allowance Calculator, and see the EU ETS allowance methodology for the benchmark and cap-decline formulas behind it.
Common Confusions
- Treating allowances as an emission reduction. Surrendering allowances satisfies a legal obligation; it does not lower the tonnes you report. This is the single most common error.
- Confusing allowances with offsets. An allowance is a permit to emit inside a capped system; a carbon credit or offset represents a reduction elsewhere. Most modern schemes admit few or no offsets for compliance.
- Mixing the cap with the tax. An ETS sets a quantity and discovers a price; a carbon tax sets a price and discovers a quantity. Calling either a “carbon tax” loosely leads to the wrong calculator and the wrong mental model.
- Reading the allowance quantity on the wrong GWP basis. A scheme’s monitoring regulation fixes its own GWP set (the EU ETS uses AR5). Do not silently convert covered tonnes to the AR6 corporate-reporting basis.
- Assuming free allocation means free carbon. Free allowances still carry an opportunity cost — an allowance not sold is revenue forgone — which is why they still shape abatement decisions.
Frequently Asked Questions
An emissions trading scheme, or cap-and-trade, is a market-based carbon-pricing policy. A regulator caps total emissions from covered sectors, issues a matching quantity of tradable allowances — one allowance permits one tonne of CO₂e — and requires every covered installation to surrender one allowance for each tonne it emits. Firms trade allowances among themselves, so abatement happens where it is cheapest and a carbon price emerges. The cap falls each year, raising the price and cutting emissions over time. The EU ETS and UK ETS are the best-known examples.
They are mirror images. An ETS fixes the quantity of emissions — the cap — and lets the market set the price of an allowance. A carbon tax fixes the price per tonne and lets emissions settle wherever that price drives them. So an ETS gives more certainty about the environmental outcome but a variable carbon price, while a carbon tax gives a predictable price but a less certain emissions result. You can model each with the EU ETS Allowance Calculator and the Carbon Tax Liability Calculator.
No. Allowances are a compliance obligation, not an inventory adjustment. The tonnes you emit are reported as Scope 1 emissions under the GHG Protocol whether or not you hold or surrender allowances. If you emit 500,000 tonnes and surrender 500,000 allowances, you still report 500,000 tonnes — the allowances were the cost you paid, not a reduction you made. Like carbon offsets, allowances are accounted for separately and are never netted against gross emissions. Only emitting fewer tonnes lowers the reported figure.
A carbon allowance is a tradable permit to emit one tonne of CO₂e within a capped scheme — the EU calls its unit the EUA, the UK the UKA. Allowances reach emitters by auction (the norm for the power sector) or by free allocation against a benchmark (for trade-exposed industry). Their price is set by supply and demand in the allowance market: because the total supply is capped and declining, the price tends to rise toward the marginal cost of abatement needed to meet the cap. Companies often use that market price to set an internal carbon price and to screen projects on a marginal abatement cost curve.
The EU ETS (launched 2005) is the oldest major scheme; the UK ETS (2021) replaced the UK’s EU ETS participation after Brexit. China’s national ETS (2021) is the largest by covered emissions, currently focused on power generation. Others include California Cap-and-Trade (2013, linked with Quebec), RGGI in the US Northeast (2009), Korea’s K-ETS (2015), and the New Zealand ETS (2008). The World Bank Carbon Pricing Dashboard tracks the full set — together, emissions trading schemes and carbon taxes now price roughly a quarter of global emissions.
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